1. Field of Invention
This invention is directed to power meters, in general, and to variable-rate watt-hour meters, in particular.
2. Prior Art
There are many known types of devices for measuring power which is used by a user. Typical of these devices is a watt-hour meter of the type which has been used for many years to indicate the cumulative energy passed through electric wires or power lines. The meter is arranged to include current coils which are connected in series with the "hot" lines from the power source. A potential coil is connected across these "hot" lines. The watt-hour meter functions to read the product of voltage, current, power factor and time. This reading indicates the energy which has been used by the user and the utility or supplier merely multiplies this number by the rate number and arrives at a billing schedule. Unfortunately this technique provides a single rate schedule with little or no flexibility in billing procedures.
In the present situation of energy shortages, there has been an attempt to encourage the use of energy at off-peak hours. This would have the effect of reducing the peak load requirements and smoothing the load requirements from the utilities. As a result more uniform energy requirements are established along with a better utilization of the utility equipment. Moreover, the need for additional utility equipment for peak load periods would be reduced.
In order to encourage this more evenly distributed usage, utilities are proposing to use different billing rates as a function of the time of day. In order to establish this variable rate structure, a "time-of-day" metering is required. In this case the customer is charged at different rates for each kilowatt-hour as a function of the time at which the energy was used.
This type of rating can be obtained by using a meter which has two or more registers to accumulate kilowatt-hours during different rate periods. However, this arrangment would require a totally new kind of meter or a plurality of meters at each installation. The cost of this method, therefore, is prohibitive. Other types of metering methods have been explored but they are equally as expensive and difficult to implement.